WASHINGTON — When FBI agents and police officers fanned out across the country last month in a week-long effort to rescue child sex trafficking victims, they pulled minors as young as 11 from hotel rooms, truck stops and homes.

Among the 168 juveniles recovered was a population that child welfare advocates say especially concerns them: children who were never reported missing in the first place.

Advocates say the roundup reinforces the need for a standardized, nationwide approach to report children as missing, especially those absent from state foster care systems who are seen as most vulnerable to abuse. Concerns over unaccounted-for children aren't new, but they're receiving fresh attention amid heightened awareness of child sex trafficking. State and federal efforts are under way to streamline how police are alerted when kids disappear.

"This has been a movement that I would say over the last year has really galvanized," said John Ryan, president of the National Center for Missing and Exploited Children. Legislation pending in Congress would require child welfare agencies to alert police and the center, which has specialized response teams and other resources, within 24 hours of a child's disappearance.

The current patchwork of state and federal policies has yielded what advocates describe as a fractured safety net with little accountability.